Generally, swimming caps are made out of materials such as silicone and latex. Although these fabrics and the tight-fitting nature of a swimming cap can cause an increase in friction to your strands, the damage caused by chlorine and saltwater is deemed far worse. Because of this it is more important to choose any type of swimming cap than none at all. Do keep in mind though that those with a lot of hair might find it difficult to cram it all into a tight-fitting swimming cap and doing so could cause damage. An example of a swimming cap that is designed to be 'safer' for your strands is the 'Bubble Cap' style, which gives a softer, more snag-free fit. It is designed to slip on easily reducing hair pull making it an ideal choice for swimmers with sensitive scalps or long hair: https://swimming-caps.info/all-star-bubble-cap-with-straps